What people in that temple do is unknown and common among people.
That is to say, although the Holy Grail has been drawn, it must be thrown into a straight and a reverse three times in a row, which shows that the drawing is accurate and is the instruction given to you by God. If you can't throw the Holy Grail into a straight and a straight for three times in a row, it means that the draw is not yours and can't guide you.